This invention relates to an electromagnetic spring clutch built into the paper feeding mechanism of a copying machine, or similar device.
The conventional electromagnetic spring clutch of the prior art includes first and second rotary members, both of which are formed of nonmagnetic materials. The first rotary member is placed around a shaft and held by a pair of snap rings. The second rotary member is placed over a portion of the first rotary member. That portion of the first rotary member is referred to as the cylindrical first bearing part, which is integrally formed in the first rotary member. The first and second rotary members rotate together by the tensioning or winding-up of a coil spring that is placed or fitted between portions of the first and second rotary members. The generation of magnetic flux which is caused by energization of a coil, causes a cylindrical armature to tension the spring.
An electromagnetic spring clutch of such construction is shown in Japanese Laid Open Utility Model No. 6-24239. The clutch fits around a shaft at a point at which the shaft is noncylindrical. A stepped outer peripheral surface is provided along a first rotary member. The second rotary member is placed along the outer peripheral surface of the first rotary member at a location called the cylindrical first bearing part. The first rotary member includes a cylindrical spring wind-up part or portion, which extends upwardly from the first rotary member with an outer diameter that is larger than that of the first bearing part of the first rotary member. The first rotary member also includes a cylindrical second bearing part, the outer diameter of which is larger than that of the first bearing part; and, a cylindrical third bearing part of the same outer diameter as that of the said first bearing part. The first rotary member is made of a nonmagnetic synthetic resin.
The second rotary member has a center hole which fits around the first bearing part of the first rotary member. Provided on the outer peripheral surface of the second rotary part is a cylindrical spring wind-up part of nearly the same outer diameter as that of the spring wind-up part of the first rotary member; a cylindrical fourth bearing part of same outer diameter as that of the second bearing part of the first rotary member; and, a gear part of larger outer diameter than that of the fourth bearing part.
A coil spring, one end of which is engaged to second rotary member, is fitted or placed between the spring wind-up parts of the first and second rotary members. A cylindrical armature is also placed around the spring and between the spring wind-up parts of the first and second rotary members. The armature has an open end at one end that engages the coil spring. The armature also is rotatably fitted (concentrically) around the shaft and rotary members along the fourth bearing part of the second rotary member and the second bearing part of the first rotary member.
In addition, a magnetic excitor or electrical winding is supported on the third bearing part of the first rotary member. The magnetic excitor has an annular first core of L-shaped cross section. A circular plate second core is fixedly attached to the open end of the first core. A bearing member with a boss part is fitted to the center hole formed in the circular plate part of the first core. An electromagnetic coil is stored in annular grooves formed in the first and second cores, and wound on the coil bobbin.
A center hole, or aperture, is formed in the circular plate second core of the magnetic excitor. This center hole, and the open end of the armature located radially inside of the coil bobbin, oppose the side force of the bearing member across an annular gap in the axial direction.
The conventional electromagnetic spring clutch of such a construction is assembled and utilized in the copier's paper-feed mechanism. Rotation of the clutch is restricted by engagement of the magnetic excitor to a stopper-pin protruding from the fixed housing. A gear part of second rotary member meshes with the gear on the drive side. When the drive side rotates, the second rotary member, coil spring, and armature rotate on the first bearing part of the first rotary member.
When the electromagnetic coil is energized under such conditions, magnetic flux flows through the first and second cores, while the bearing member and armature are magnetically attracted or suctioned into the bearing member which causes it to be stopped or braked. In this manner, the coil spring is wound around the spring wind-up parts of the first and second rotary member because of the rotation of the second rotary member. Therefore, under such magnetic excitation conditions, or energization of the coil, the drive side rotation is transmitted to the driven rotary shaft. When the electromagnetic coil is not energized, the rotation-transmission to the driven rotary shaft is cut off because braking of the armature is released.
Japanese Laid-open Patent No. 63-293327 and Laid-open Utility Model No. 63-187729 also explain such an armature-braking-type electromagnetic spring clutch.
The armature-driven-type electromagnetic spring clutch is also conventional and part of the prior art. In general, in the armature-braking-type electromagnetic spring clutch, an armature rotates along the bearing member of the magnetic excitor. The rotation of the excitor is restricted by a fixed housing, which is made of ferro-magnetic materials. Therefore, the wear particles generated by the bearing member's frictional engagement with the armature interfere with long-duration maintenance of stable operation of the electromagnetic spring clutch.
Japanese Laid-open Patent No. 63-293328 proposes an armature-driving-type electromagnetic spring clutch that solves this wear problem. That is, the noncylindrical surface, which is the outer peripheral surface of the first rotary member, is formed between the spring wind-up part and the third bearing part and a circular plate rotor. A similarly shaped center hole is formed in the fitting surface, and is press-fitted to the fitting surface. The armature is magnetically attracted to the rotating rotor by the magnetic flux of the electromagnetic coil. As a result of this attraction, the coil spring is wound up on the spring wind-up parts of the first and second rotary members for transmission of the rotation of the driving side rotary shaft to the second rotary member. The armature-driving-type electromagnetic spring clutch can maintain stable operation for a long duration compared to the armature-braking-type electromagnetic spring clutch when used in the copier paper-feed mechanism, because the load on the driving-side second rotary member is light and generation of wear particles due to rotor-armature frictional engagement is less.
In the conventional electromagnetic spring clutch, the bearing parts of second rotary member and magnetic excitor contact the first rotary member, which is formed of a nonmagnetic material, such as synthetic resin. The bearing parts that support the armature are along both the first and second rotary member. The armature-driving-type electromagnetic spring clutch thus has a construction in which a rotor is press-fitted onto the outer peripheral surface of the first rotary member. However, such a construction needs to be improved in order to offer the device at a lower cost because the bearing member contacts the magnetic excitor in the conventional electromagnetic spring clutch.
Also, improvement of the armature-driving-type electromagnetic spring clutch is necessary because its axial length is too long due to the axial annular gap formed between the bearing member of the magnetic excitor and rotor. In addition, the outer size of the magnetic excitor of this type of electromagnetic spring clutch is too large in general because the pair of lead wires are taken outside from the inside of the magnetic excitor by individually connecting the start and the end of the winding of the electromagnetic coil to the lead wire, so that the construction needs improvement in order to reduce the size.
The present invention is directed to an improvement over the described conventional electromagnetic spring clutches.